1. Field of the Invention
The present invention relates to an electromagnetic flowmeter which is capable of measuring the flow rate of a fluid that flows in the interior of a flow passage.
2. Description of the Related Art
Heretofore, for example, an electromagnetic flowmeter has been known in which, by energizing coils, a magnetic field is formed in a flow passage through which a fluid flows, and the flow rate of the fluid is calculated based on an electromotive force generated in accordance with the conductivity of the fluid that flows through the flow passage.
Such a flowmeter, for example as disclosed in Japanese Patent No. 4591015 (Patent Document 1), is equipped with a measurement conduit through which the fluid is guided, a pair of electrodes mounted on an outer side of the measurement conduit, and a pair of excitation coils and a pair of cores, each pair being arranged perpendicularly with respect to the electrodes on the outer side of the measurement conduit. Additionally, a magnetic field generated by the excitation coils is formed perpendicularly with respect to the measurement conduit, and an electromotive force, which is generated in the fluid by the pair of electrodes, is extracted and converted by a controller into a flow rate of the fluid. Further, in such an electromagnetic flowmeter, a flow passage formed in the interior of the measurement conduit is formed such that an inlet port and an outlet port in an axial direction thereof are formed with circular shapes in cross section, and an intermediate region in the axial direction is formed with an elliptical shape in cross section. The two excitation coils are thereby arranged in close proximity at the intermediate region with a gap between the excitation coils being kept small, so that magnetic losses are minimized, and thus a large signal can be obtained with low power.
Further, with the electromagnetic flowmeter disclosed in Japanese Patent No. 5102463 (Patent Document 2), a yoke lid is fastened to an upper part of an excitation plate on which excitation coils are mounted, an outer peripheral region of a measurement conduit is thereby surrounded by a metallic member, and a magnetic circuit is constructed by a magnetic field generated by the excitation coils.